Wax is added as a blending material to be added to an oil-based ink composition for use in writing instruments such as an oil-based ink pen or an oil-based ball point ink pen and desk supplies. Wax is also used in ink for a writing instrument for various purposes utilizing solubility and interfacial film formability. Such an example is described in Japanese Unexamined Patent Publication (Kokai) No. 11-335612, Japanese Unexamined Patent Publication (Kokai) No. 2001-240788, Japanese Unexamined Patent Publication (Kokai) No. 2003-213162 and Japanese Unexamined Patent Publication (Kokai) No. 11-92706.
It is described in Japanese Unexamined Patent Publication (Kokai) No. 11-335612 that a wax oxide is added to an ink composition in order to prevent dry-up when a quick-drying oil-based ink pen is allowed to stand in a state where the cap has been removed, and also discloses that wax oxide is added to the ink composition by merely mixing.
It is described in Japanese Unexamined Patent Publication (Kokai) No. 2003-213162 that paraffin wax is added to correction fluid in order to prevent drying of the tip of a writing instrument type correction device, and also discloses that paraffin wax is added to the ink composition by merely dissolving the paraffin wax and then mixing, it with the correction fluid.
It is described in Japanese Unexamined Patent Publication (Kokai) No. 11-92706 that writing feel is improved by adding a wax having a melting point of 60 to 100° C., specifically carnauba wax, Montan wax or the like to an oil-based ink composition for a ball point pen, but does not describe a specific method of adding these waxes.
When wax-based substances such as polyethylene wax are used in a writing instrument, it is difficult to uniformly mix these waxes with an oil-based ink composition in view of the interfacial film formability and the blending method for dissolving these waxes.
Depending on the presence of the interfacial film formability or the dissolved state of the wax, a wax film may be produced on the vapor-liquid interface of the ink during storage caused with when not used over a long period of time, or caused by a difference in the temperature of the ambient environment, and sediment may also be produced as a result of interaction with raw materials in the ink. Furthermore, a problem may occur when the wax is converted into an undissolved lump or sedimentation of the wax, since wettability of wax with an ink solvent wax is inferior.
Generally, when wax is introduced into an oil-based ink composition, the wax forms a film, which is a foreign matter to the ink composition. Therefore, wax is dispersed so as not to form a film in the ink composition. It has been found that the various problems described above when using a wax-based substance in an oil-based ink composition for a writing instrument are caused by poor stability of a wax dispersion dispersed in the ink composition.
An object of the present invention is to provide an ink composition containing an olefinic wax dispersion added in order to impart smooth writing properties without causing ink starving at the starting of writing, and the ink composition having noticeably improved stability over time.